It has heretofore been proposed, for example as shown in U.S. Pat. No. 3,908,564, to form a shelf apparatus in which a plurality of generally rectangular frames are hingedly interconnected at their upright portions to form a polygonal frame module, and to stack one or more such polygonal frame modules one on top of the other. In U.S. Pat. No. 3,908,564, a shelf is provided with a downwardly opening channel along its side edges which is dimensioned to receive adjacent horizontal members on the upper and lower frame modules, to interconnect the stacked frame assemblies. However, the contiguous horizontal members on the upper and lower frame shelf assemblies are received within and concealed by the downwardly opening channel on the shelf. Moreover, while the downwardly opening channel on the shelf inhibits relative horizontal movement between the upper and lower frame modules, it still permits vertical separation so that upper frame modules of the stacked shelf apparatus can be dislodged by tipping relative to the lower frame modules, if the upper frame modules are bumped or pushed laterally.